Alternating current clock



July 2, 1929. L. HAMMOND ALTERNATING CURRENT CLOCK Filed May 20, 1929 2 Sheets-Sheet l July 2, 1929. L. HAMMOND ALTERNATING CURRENT CLOCK Filed May 20, 1929 2 Sheets-Sheet 2 Patented July 2, 1929.

UNITED STATES PATENT oFEicE.

LAURENS HAMMOND, oF WINNEIKA, ILLINOIS, AssIGNoR To THE HAMMOND CLOCK COMPANY, or CHICAGO, ILLINOIS, A CORPORATION or ILLINOIS.

.ALTERNATING-CURRENT CLOCK.

Application filed May 20,

- from minute to minute, the frequency is governed so that the total number of alternations per given period, suoli as an hour, is exactly uniform. Thus, for example, in the power supplied the frequency may vary slightly 'above and below 6() cycles per second but the average number of cycles per second will be maintained at 60. A synchronous motor driven clock supplied with current from a source at which the frequency is thus carefully regulated, may be made to indicate the correct time excepting only such slight discrepancies as may result from slight variations in the frequency of the current. 7With present equipment and cont-rol mechanism, this Variation is not cumulative, so that the inaccuracies in time indication by synchronously driven clocks is so small as to be ol' negligible importance in clocks used for ordinary purposes.

VSynchronous motor driven clocks of a type adapted to be used in .sys-tenis as above described have been known and in use for a long time. My invention consists of the improvement of. clocks of this type to make them more reliable.y more simple in construction and less lialoleyto be affected by variations in the current supply.

It is a primary object of my invention to provide an improved non-self-starting synA chronous motor driven time indicating device which may be easily manually started and which, if started at a speed higher than synchronous speed, will, as it drops to Syncronous speed, automatically get in step and thereafter maintain its exact synchronous speed. 1

A further object is to provide an improved synchronous motor which, although not selfstarting, may easily be manually started.

A further object is torprovide an improved synchronous motor which, if launched at a pe d greater than the. synchronous speed byY an external source of power, will, as it slows "own to the synchronous speed, fall into step 1929. Serial-No. 364,480.

and continue in operation at synchronous speed.

A further object is to provide an improved inertia means applicable to thevrot-or of a synchronous motor which will be effective to aid In maintaining the rotor at synchronous speed. Y

A further object is to provide an improved synchronous motor in which an improved form of friction inertia means having a coefliclent of friction varying with the relative speed between the rotor and inertia means, is utilized.

A further object is to provide an improved synchronous motor having an inertia member loosely coupled to the rotor of the motor by a frietional hydraulic means.

Other objects Will appear from the following description, reference being had to the accompanying drawings, in which Fig. 1 is a front elevation of my improved clock mechanism, portions ofthe dialand gears being broken away show the Linderlying parts;

Fig. is a bottom plan view thereof, with the dialshown in section;

Fig. 3 is a vertical sectional-view taken on the line 33 of Fig. 2; and

Fig. l is an enlarged ,vertical section taken on the line 4 4 of Fig. showing particularly the rotor andthe rotor inertia membe As best shown in Figs.. l and the clock of my invention comprises the usual front and rear frames 8 andi() which are held in spaced relation by four bolts 12. The clock is driven by a synchronous motor, hereinafter described in detail, which has a. shaft 16 carrying a driving pinion 18. rthe pinion 18 meshes with a gear 20 rigidly mounted on a shaft 22. The shaft 22 also carries a pinion 24. which .meshes with a gear 2 6 carried on a shaft 28. A pinion 30, rigidly secured to the gea-r 26, meshes with a gear 32 carried on a shaft 34 which is journaled in the frames 8 and l() and at its forward end carries a second hand 36. The minute vhand 38 and hour hand 40 are suitably driven through a train of gearing which derives its pon'er from the shaft 34, as is Well known in the art. The hands 36, 38 and 40 register With a suitable dial 42 which may be supported by the frame 8 or by the casing of the clock in any suitable manner.

igidly secured to the vforward end of the rotating shaftv Q2 is a segmental disc 44 1which llO core which is suitably bolt-edtothe iframe` 10. A plurality of the laminations of the core 50 project upwardly to form 4a pair of pole pieces 52 which extend into close propin'quity with the periphery of a magnetic rotor 54. The rotor 54 has a plurality of A regularly spaced radial projections 56 which are so spaced that. two non-adjacent projections may lieY in substantial registry with the pole pieces 52at one time.

The rotor 54 is pressedover .the reducedA end of a non-magneticsleeve or hub '58' which in turn Ais secured over the enlarged portion 60 of thev shaft 16. 1 The sleeve 58 vforms the hub'foi` a casing 62 'formed in' two halves 64 which are soldered ltogether at their peripheries at 66 and also to the hub 58. VVi'thin the casing 62 is a pair of non-magnetic washers or `inertia vmembers (38 which are mounted for free rotation relative to theA hub 58 andrelative to eachother. -'Ilie easing 62,'is filled, eithercom-pletelyon partially, with oil or other suitable semiviscous liquid. This liquid not only 1forms a frictional connection between thel washers 68 and the casing butiits mass also adds. tothe inertia of the members 68 and'has an effect similar to that ofthe washers. In fact, I have found that the washers 68 'may be omitted and liquid only used as the inertia substance in the casing, With'satisfa'ctory results. Thus when I hereinafter refer to an inertia member? which is frictionally coupled with the rotor shaft, I wish it to be understood that I include. not only such Ameans as the washers 68 but also oil or other fluid which will normally bemoved by the shaft'but which is capable of 'independent motion,. and other equivalentmeans.

The ends ofthe shaft 16 have portions 70 of reduced diameter which 'are journaled in suitable bearingsvformed in plates 721 The bearing plates-72' have sidewardly extending Y bosses74 which project into suit-able apertures formed in the frames 8 .and 10 and are riveted tov the frame Y. by having a flanged portion 76 i extending` from. the boss 74, swaged or riveted against. the frame.

Cup'sha-ped oil.reservoirs 78 are'` suitablyl secured to the bearing-.plates 72 by Vhaving their brims pressedy over ands'oldered to the plates. The .plates 72 have vertical grooves 8OV of capillary dimensions formed in their outer faces. These groovesserve as .oil ducts to insure a continuous supply of lubricant to the end bearings of the shaft 16 as long asany oil remains in the reservoirs.

Thereservoirs78 preferably have vertical grooves 82 depressed therein. The reservoirs, together with the bearing plates 72,

are assembled with the jroovcs8()y and 82 in alignment so that these subassemblies may readily be secured to the frames in such po sition that the groovesl are vertical.

The shaft 22 at its rearward end has a suitable thumb nut 84 by which the clock may be manually started. The hands of the cloelc may be setby a suitable thumb nut 86 which is connected to the hands through the usual means.

In order that the clock may be easily started, it is necessary that a peculiar relationship exist between (1) the energy or force required to pull the rotor out of step, (2) the frictional resistance to motion of the inertia members relative to the shaftlG, and (3) the frict-ional resistance of the load which comprises the friction in the time gear train and the friction at the end bearings of the shaft 16'.

The total friction ofthe load and of the bearings of the shaft-16 should'be-less than the friction (2) between the inertia members 68 and the shaft 167 and the friction between the inertia members 68 and the shaft 16 should be less than the force (1) required to pull the rotor out of step. Naturally the frictional resi-stance (8) of the load must be less than the force (1).

The relationships above-described constitute one of the essentialfe'atures of my invention. I am aware that it has been proposed and is old in the art'to have an inertia member frictionally driven by a synchronous motor or other prime mover which runs at a. speed alternately greater and less than an 1 average running speed. Such synchronous motors or other prime move-rs, which may vary in speed in a manner usually referred to as limiting, have been equipped with inertia `members driven by friction meansfo'r the purpose of preventing such hunting. In these prior arrangements the frictional work done between the prime mover and the inertia member is work which is done at the expense of the `forces tending to produce hunting. If such arrangements were to be madeto synchronous motorsl for such purpose. it is obvious that the internal friction-al work done in the anti-hunting devices should be small compared to the useful werk done on the load of the motor. The same would of course apply'to similarantiliunting de- Ill) iffifreo and the rotor greater than the total load, and still not tiX the inertia members so rigidly to the rotor that occasional relative motion between the two results, in the process of starting' and synchronizing' the clock and in cases of sudden electrical distnrlnincesy or brietI interruptions of the power supply. This will be made clearer in the following` description of the operation of the motor.

The alternating currentpassingrthrough the coil 48 produces a magnetic tlux in the core 50, the linx circuit of which is completed through the pole pieces 52 and portions of the armature or rotor 54. This linx varies in density and direction in accordance with the current flow through the coil 48. The projections 56 on the periphery of the rotor 54 are successively attracted toward the stationary pole pieces 52 during normal running at synchronous speed. The operation of motors of this type is old and well known and need not be further explained herein. 'lhis typ-e of motor is not self-starting' and when it is not equipped with my improved inertia and friction device it is difficult to start and is also unsatisfactory in other ways. With seine practice it is possible to start such a motor manually, provided that it is caused to rotate at the exact synchronous speed at which it Will run thereafter and is left running; in a position which may be said to be in step. If such a motor is manually launched to a speed greater than synchronism and then allowed to slow up of its own accord, it will not rcmain running at synchronous speed although it obviously must have been running at exactly the right speed at some time durine` this operation. This is became al' thc instant when it was running' at the exact synchronous speed it was not in step" lt'such a motor is launched. it will not necessarily continue to rnn indefinitely because ot` the fact, that disturbances in the power supply. such as harmonics` and surges on conunercial lighting lines. may'cause it to hunt to such an cxtent that it will fall out of step and suddenly stop.

The use of that type of motor in synchronous clocks is old and is not claimed by me cX- cept in conjunction with my improved frictional inertia device.

lYhen such a motor is equipped with the frictionally driven inertia member as described heretofore and the friction between the rotor and the inertia member is made greater than the torque of the load which itself has little inertia. the behavior on starting is entirely different. To start the motor under these circumstances, it is only necessary to impart to it by manual meaigis a speed of revolution greater than synchronous speed. The friction between the rotor and inertia member is great enough so that during;-

this manual impulse not only the rotor, but

also the inertia member, is caused to revolve at a speed greater than synchronism. lVhcn the motor now starts to slow np and approach synchronous speed7 itfalls into step with a sudden motion in which slipping occurs between the rotor and inertia member, whereupon internal frictional work is done,vand this work is greater than the work of the total load duringT the same interval of time. The theory is amply borne out by the fact that in practice the motors of my invention invariably start from superspeed. whereas motors of the same type. without this device, do not.

l am of course a 'are of the fact that it has been in'oposed to malte synchronous motor driven clocks which wll come into synchronism when launched at a speed greater than s vnchronism, by means of inertia members, the moment of inertia of which is variable. but such devices come into synchronism only when there happens to be a sp-ecitic position of the members at the instant the rotor falls into step, whereas the inertia member of my invention is always in position to assist the rotor to come into step.

The motor herein described will also come into synchronism and continue to operate if launched at a speed slightly less than synchronous speed. The inertia and friction members (38 will also have an effect, in maintaining` the rotor in step when there are short interruptions. in the supply of current, and during such brief interruptions the momentum of the inertia members, together with tue fact that the friction between these members and the shaft is greater than the load` enable, them to carry the load durin`r the brief interruption.

lt will be noted that the friction between the membersy titi and th:l rotor shaft lt is not coin-dant but increasesy with the diti'crcnce in speed between the-e member.y and the shaft, duc to the fact that llu` greater part of the friction is caused by the shin friction and internal friction ot the lil uid contained in the casing tif. Thus. npon a slight acccleratii'sn of he rotor. the energy dissipated and the torque furnished by the rotor to the members o3 andthe liquid within the casing' o2 will be an extremely small amount, but as the a celeration of the rotor becomes greater the encrn'y thus lost by friction. and consequently the torque applied to the inertia members, will he very much greater: and conversely. it' the rotor tends4 to clccelerate rapidly tln` eneigwv which will be returned to the rotor shaft from the inertia nnmbers (SS will be correspoiulinn'ly very great, while for a slight deceleration Ihe rotor the energy returned to the rotor bv the inertia members G8 will he corresponr'lintrly very slipjht. Ythis type of frictional connection between the rotor shaft and the ineria member is a substantial factor in malringr the cloctv of my invention ,so caf-"f to start anfl in making' the motor keen in step so perfectly. Since the thumb piece llt) Cit

ort is geared to the rotor shaft so that slovv rotation of the former will cause rapid rotation of the latter, a single twirl of the thumb piece vvill impart to the inertia member, due to the particular t'vpe of its it'rictioual conneetion vvith the rotor shaft7 a speed of rotation suficient so that the momentum or inertia of the inertia member vvill be capable, of driving the roto and the load at a speed above s vnchronism.

A practical and simple test for determining the proper values of friction and povvcr ma;Y be made in the following manner: IVith the current shut oli' and all parts at rest', turnhn.;vl the inertia member bv an outside force will revolve the rotor and the entire gear train. Vith the current turned on and allA parts a tr rest. the rotor vvill be automati 'all'v locked into one oosition and the inertia member may be revolved from an outside source vvithou?` causing an v other members to move. pro vided that this is not done too rapidly.

Various constructiomil details disclosed in this appiication are not elainied herein but are described and claimed in other co-iliendH ing appli atfions tiled bv me.

`he invention is capable of n'ide Yariation vvithin equi valentf limits and I contemplate such variation as may be desirable or use ful in the particular adaptation of the invention shovvn. or in its adaptation to other de vices.

I do not restrict m'vseltl in an)v unes i particulars. but what I claim and desire to secure bv Letters Patent is:

l. In a time-keeping device having` a `gear train. a s vnchronous motor having a rotor` and an inertia element frictionallv connected to the rotor. the torque due to friction between si id element and said rotor beino suliicient to drive the gear train but insutlicient to drive said train and to move said rotor out of stop. the values of the inertia. the load and the Vtrietional torque being such that when said rotor is launched at a speed greater than vin ehronous speed it will automatieallv start operation at synchronous speed when it slows dovvn to said speed.

2. The combination of a non-self-stariing s vtnhronous motor having a rotor and a load of relativel),v small friction and small inert iat and an inertia element frietionallv connected to said motor. the torque due to friction between said inertia element and said rotor being greater than the load and the friction of the motor. the values ofthe inertia. the load and the frietional torque being such as to cause the rotor to come into s vnchronism .vhen launched at a speed greater than s vm-hrenisui.

3. In an alternatingl current clock having a gear train. the combination of a synchronous motor ha 'ine` a rotor for driving the gear train` pole pieces for said rotor. means to produce a var'ving flux across said pole pieces'` an inertia member rotatable relative to said rotor, and friction means normally tending` to prevent such relative rotation, said triction means having a coetlicicnt of friction sutlicicntljvv high and an area of contact sufficiently great so that said member may transinit enough of its energy to said train to drive the latter at substantially synchronous speed during brief current interruptions.

ft. A synchronous motor comprising a rotatabie armature. a shaft geared to said armature so as to rotate at a substantially lesser speed. mamiallv engageable means for rotating said shaft. an a friction and inertia dovice adapted to be rotated bv said armature or b v said manually engageable means, the inertia of said devic and the coefficient of friction between it and said armature being sutlieient to permit said device to drive said armature at substantiallvY synchronous speed for a brief interval. vvlxcrcbv said device may be brought to a speed higher than the s vnehronous speed of said armature b v a single manual operation of said means and the coetiicient` of friction being of such value that said device and said armature will decelerate at sibstantiallv the same speed. the only substantial deviation in the speeds of said device and armature occuring as the armature tirst reaches substantially synchronous speed.

In a time-keeping device having a gear train. the combination of a synchronous motor operable from a commerial source of alvernating current and having a shaft with portions of small diameter at its extremities. hearings for said portions. a magnetic, substantially circular rotor having teeth formed thermin,y a pinion secured to said shaft for driving said train. a circular inertia member mounted on said shaft and rotatable relative to said rotor. and means for causing more friction between said inertia member and the rotor than exists in said bearings.

6. In a time-keeping device comprising a gear train. the combination of a synchronous motor iperalne from a commercial source otl alternating current for driving said train, said motor having an armature shaft with portions of different diameters. bearings for receiving the portions of smaller diameter, and an inertia member rotatablyv and fric-v tionall'v mounted upon thel portion of larger dianrter. the quantitative relationship between said elements being such thatl the frietion of said shaft in said bearings constitutes an apln'eeiabie portion of the load of said mo tor. and the frictional torque of said inertia member is greater than the torque due to the friction of said bearings and of said train.

7. In a time-hee )ing device comprising a gear train. the combination of a synchronous motor operable from a commercial source alternating current driving said train. said motor having an armature shaft. bearings therefor. and an inertia member mounted on said shaft and movable relative thereto, the mounting of said member being such that the lOl) llt)

energy capable of being dissipated by friction upon movement ot' said member relative to said shafts is greater than the energy lost in friction in said sha'tt bearings and in said gear train.

8. ln a time-keeping device comprising a gear train, the cmnbination of a synchronous motor operable from a commercial source ot alternating current connected to said train, said motor having a rotor, a support therefor, and an inertia member normally rotating with said rotor but capable` ot' Vangular displacement relative thereto, the torque due to the friction between said rotor and said member being greater than the combined torque due to friction betwen said rotor and its support and the t'riction ot said train.

9. In a time-keeping device having a gear train and adapted to be driven directly `trom an alternating current source the Combination ot' non-seltstarting synchronous motor having a rotor adapted to drive the gear train` a manually engageable member geared to said rotormthe gear ratio between said member and said rotor being sutiiciently great so that when said member is manually twirled at a speed easily obtainable by a single manual operation the speed ot' said rotor will be above its synchronous speed, and inertia means trictionally connected to said rotor, the quantitative relationship between said means, the load imposed by said gear train, and the magnetic forces acting on the rotor being such as to cause said rotor to tall into step and continue operation at its synchronous speed when it arrives at said speed due to deceleration caused by the load.

l0. In an electric clock having a time gear train and adapted to be driven directly trom an alternating current source, the combination ot' a non-sel-starting synchronous motor having a rotor, a manually engagcable member geared to said rotor, the gear ratio between said member and said rotor being sutticieutly great so that when said member is manually operated a a speed easily obtainable by a single operation` the speed ot' rolation ot said rotor will be above its synchronous speed. an inertia element rotatable relative to said rotor` and a trictional driving connection between said element and said rotor. the (piantitative relationship between said connection, the inertia of said element, and the load imposed by said g\ar train being such that said rotor will automatically fall into and maintain its synchronous speed as it slows down trom the speed above synchronism at which it was launched.

ll. ln an electric clock having a time gear train and adapted to be driven directly from an alternating current source, a non-seltstarting synchronous motor having a rotor, means actuated by a single manual operation for imparting to said rotor a speed greater than its synchronous speed, an inertia element rotatable relative to said rotor, and a liquid forming a trictional driving connection between said element and said rotor, said connection having sufficient friction at the speeds which are attained so that said rotor will tall into step and continue operation at synchronous speed as it slows down trom the greater speed at which it is manually launched.

l2. ln an electric clock having a gear train and adapted to be driven directly from an alternating current source, a non-selfstarting synchronous motor having a rotor, means actuated by a single manual operation for imparting to said rotor a speed greater than its synchronous speed, an inertia element rotatable relative to said rotor, and a liquid forming a frictional driving connection between said element and said rotor, said connection being capable ot' transmitting suticient energy trom said element to said rotor to drive said rotor and the gear train at substantially synchronous speediduring a brief interrup-l tion in the supply ot current from said source.

13. In au alternating current clock havingl a timey gear train, the combination ot a synchronous motor havingl a rotor tor driving said train and adapted to be driven from a commercial source ot alternating current., and an inertia element frietionally connected to said rotor and movable relative thereto, the friction between said rotor and said element being greater than the total friction of the rotor and said train.

14. 1n an alternating` current time-keeping device having a gear train, a synchronous motor for driving said train, said motor having a rotor, and an inertia element trictionally connected to said rotor, the friction between said element and said rotor being sutiicient to drive said train when said element rotates relative to said rotor at the speed obtained when the rotor decelerates from super-synchronous to synchronous speed due to the load.

l5. ln a time keeping device having a load of relatively small inertia and a small amount olI l'rictiou` a synchronous motor for driving said load. said motor comprisil'ig a magnetic rotor,polc pieces therefor, means to produce a varying flux across said pole pieces. an imperforate casing tiXed relative to said rotor. an inertia element and a liquid both contined within and movable relative to said fasing, said element having sutlicient inertia and said liquid causing sufficient friction so that said element will be capable of driving said rotor and said load at substantially synchronous speed tor a short time, and means for manually imparting to said rotor a speed greater than its synchronous speed.

16. In an alternating current clock having a gear train a synchronous motor for driving said train, said motor comprising a rotor connected to said train, and an inertia element frietionally connected to Said rotor but movable relative thereto. the 'friction between said rotor andy Said element` being Sut- 'lieient at the relative speeds ordinarily obtained to drive said train but insuflirient to move Said rotor out ot' step when the latter is operating at Synchronous speed.

1T. ln an alternating current. time-keeping devi e having a gear train, the combination of a .synchronous motor having a rotor 'for driving said train, a casing containing a liquid, said easing being impertorate and rigidly eonnerted to said rotor, a plurality ot' inertia elements ronlined within and movable relative to said easing, and means t'or impartingr to said rotor a speed greater than itl synchronous4 speed by a single manual operation.

18. In a time-keeping device having a gear train, a synchronous motor adapted to be driven 'from an alternating` current source and having a rotor tor driving said train, an inertia member, and a liquid interposed between said rotor and said member and torming a trietional drive connection therebetween, said member having` suttieient inertia and said liquid being capable ot' transmitting sutlicient frietional torque so that said rotor Will7 upon a brief Current interruption, be maintained by said member at a speed aut'- tiriently Close to its synchronous speed to enable it to step into synchronous ypeed after said interruption.

Vln witness whereof, I hereunto subscribe my name this ltth days; ot' May. 1921).

LAURENS HAMMOND. 

